Interoception

What it is

The sense of the internal state of the body: heartbeat, breathing and air hunger, gut sensation, temperature, muscular tension, hunger, thirst, nausea, arousal, the vague pressure or lightness in the chest that accompanies emotion.

It is a genuine sensory system, not a metaphor. It has its own receptors, its own ascending pathway, and its own cortical territory — and most people have never been taught to attend to it systematically, which is why its findings feel exotic when they arrive.

This article closes the section because it is the most plausible answer to the question every other page here has raised: what is actually being felt?

Where it came from

The scientific account is recent. Interoception was long treated as marginal — the unglamorous business of visceral regulation — and its promotion to a full sensory modality owes a great deal to the neuroanatomist A.D. "Bud" Craig, whose work from the late 1990s traced a distinct pathway.

Signals from small-diameter fibres throughout the body ascend via lamina I of the spinal cord and the thalamus to the insular cortex, where they are progressively re-represented. Craig argued that the anterior insula, particularly on the right, is where these representations become the felt, subjective sense of one's own condition — and therefore central to the experience of emotion and of being a self at all.

The philosophical lineage is older. William James and Carl Lange proposed in the 1880s that emotions are the perception of bodily changes — that we do not tremble because we are afraid but are afraid because we tremble. Antonio Damasio's somatic marker hypothesis revived a version of this in the 1990s. On these accounts, reading the body is not incidental to emotional life; it is emotional life.

How it is used

In research, interoception is measured in several ways, and Sarah Garfinkel and Hugo Critchley's framework distinguishes them usefully: accuracy (can you actually count your heartbeats correctly?), sensibility (how attuned do you believe you are?), and awareness (does your confidence track your accuracy?). These come apart. People who believe they are highly attuned are frequently not, which is itself a finding worth carrying into every claim in this section.

In clinical practice, interoceptive training is used in anxiety and panic disorder, in eating disorders — where the signals of hunger and satiety may be poorly read — and in work on alexithymia, difficulty identifying one's own emotions.

And in the traditions, systematically and for a very long time. Yogic, tantric, Daoist and Sufi practice all consist substantially of directing sustained attention to specific internal locations and reporting what is found there.

What we can and cannot say

We can say the sense is real, mapped, measurable and trainable. That much is settled.

We can say it plausibly accounts for the phenomenology this whole section has been describing. Sustained attention to an internal location produces detailed sensation at that location. Attention shaped by strong expectation about what should be there produces sensation matching the expectation. Breath work amplifies the signal by changing the state being sensed. Prolonged practice appears to change how these signals are processed. Everything the traditions report — heat, streaming, pressure, movement, concentration at points — is within what an attended interoceptive field can deliver.

That is a substantial concession, and it should be read as one. The practitioners were not imagining things. They were doing systematic phenomenology of a real sensory channel, centuries before anyone had a name for it, and the consistency of their reports within a tradition is what you would expect from people trained to attend in the same way.

We can say it does not validate the anatomy. Interoceptive sensation is not evidence of channels, centres or circulating substance any more than the experience of colour is evidence that objects are coloured. The felt map and the physical map are different things, and the tradition's error was to assume the first was a report of the second.

We can say the evidence on expert meditators is messier than expected and worth reporting honestly. Studies comparing long-term meditators with controls on heartbeat-detection tasks have produced mixed results, with several finding no advantage — which sits awkwardly with claims of exceptional bodily awareness, and suggests that what practice trains may be the relationship to internal sensation rather than raw detection of it.

We cannot say interoception explains everything on these pages. What can be said is that a site which had reported "no evidence" on every claim in this section without naming what people are genuinely feeling would have been telling only half the story — and the half it left out is the part that made the traditions worth building.

Further reading

• A.D. Craig, How Do You Feel? (2015) — the neuroanatomy, from the researcher who assembled it.
• Garfinkel et al., "Knowing your own heart" (Biological Psychology, 2015) — the three-dimensional measurement framework.
• Norman Farb and colleagues on interoception and contemplative practice.